Carboxylic/sulfonic/quaternary ammonium polymers for use as scale and corrosion inhibitors

ABSTRACT

The instant invention is directed to a process for inhibiting corrosion and the formation and deposition of scale in aqueous systems, comprising adding to the system at least 0.1 ppm of a water-soluble polymer having an intrinsic viscosity of 0.05 to 2.5, prepared from: 
     (a) 50 to 90%, by weight, of an unsaturated carboxylic acid, or its salt; 
     (b) 5 to 40%, by weight, of an unsaturated sulfonic acid, or its salt; and 
     (c) 5 to 40%, by weight, of an unsaturated quaternary ammonium compound. 
     The instant invention is also directed to a water soluble polymer, having an intrinsic viscosity of 0.05 to 2.5 prepared from: 
     (a) 50 to 90%, by weight, of an unsaturated carboxylic compound selected from the group consisting of acrylic acid, methacrylic acid, their salts and mixtures thereof; 
     (b) 5 to 40%, by weight, of an unsaturated sulfonic compound selected from the group consisting of 2-acrylamido-2-methylpropylsulfonic acid, 2-methacrylamido-2-methylpropyl sulfonic acid, their salts and mixtures thereof; and 
     (c) 5 to 40%, by weight, dimethyl diallyl ammonium chloride, diethyl diallyl ammonium chloride and mixtures thereof.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,928,196 discloses the use of a copolymer of2-acrylamido-2-methylpropylsulfonic acid and acrylic acid in inhibitingscale.

Most industrial waters contain alkaline earth metal cations, such ascalcium, barium, magnesium, etc. and several anions such as bicarbonate,carbonate, sulfate, oxalate, phosphate, silicate, fluoride, etc. Whencombinations of these anions and cations are present in concentrationswhich exceed the solubility of their reaction products, precipitatesform until these product solubility concentrations are no longerexceeded.

For example, when the concentrations of calcium ion and carbonate ionexceed the solubility of the calcium carbonate reaction products, asolid phase of calcium carbonate will form.

Solubility product concentrations are exceeded for various reasons, suchas partial evaporation of the water phase, change in pH, pressure ortemperature, and the introduction of additional ions which forminsoluble compounds with the ions already present in the solution.

As these reaction products precipitate on surfaces of the water carryingsystem, they form scale or deposits. This accumulation preventseffective heat transfer, interferes with fluid flow, facilitatescorrosive processes, and harbors bacteria. This scale is an expensiveproblem in many industrial water systems causing delays and shutdownsfor cleaning and removal.

Scale-forming compounds can be prevented from precipitating byinactivating their cations with chelating or sequestering agents, sothat the solubility of their reaction products is not exceeded.Generally, this requires large quantities of chelating or sequesteringagent as cation, since chelation is a stoichiometric reaction, and theseamounts are not always desirable or economical.

Almost 50 years ago, it was discovered that certain inorganicpolyphosphates would prevent such precipitation when added in amountsfar less than the concentrations needed for sequestering or chelating.By polyphosphates, we mean phosphates having a molar ratio of metaloxide:P₂ O₅ between 1:1 and 2:1.

When a precipitation inhibitor is present in a potentially scale-formingsystem at a markedly lower concentration than that required for(stoichiometric) binding of the scale-forming cation, it is said to bepresent in "threshold" amounts. See for example, Hatch and Rice,"Industrial Engineering Chemistry", Vol. 31, pages 51 to 53 (Jan. 1939);Reitemeier and Buehrer, "Journal of Physical Chemistry", Vol. 44, No. 5,pages 535 to 536 (May 1940); Fink and Richardson, U.S. Pat. No.2,358,222; and Hatch, U.S. Pat. No. 2,539,305.

Generally, sequestering takes place at a weight ratio of thresholdactive compound to scale-forming cation components of greater than about10:1, depending on the anion components in the water. Thresholdinhibition generally takes place at a weight ratio of threshold activecompound to scale-forming cation components of less than about 0.5:1.0.

Certain water soluble polymers, including groups derived from acrylamideand acrylic acid have been used to condition water containingscale-forming compounds. As for example, see U.S. Pat. Nos. 2,783,200;3,514,476; 2,980,610; 3,285,886; 3,463,730 and 3,518,204.

DESCRIPTION OF THE INVENTION

The instant invention is directed to a process for inhibiting corrosionand the formation and deposition of scale in aqueous systems, comprisingadding to the system at least 0.1 ppm of a water-soluble polymer havingan intrinsic viscosity of 0.05 to 2.5, prepared from:

(a) 50 to 90%, by weight, of an unsaturated carboxylic acid, or itssalt;

(b) 5 to 40%, by weight, of an unsaturated sulfonic acid, or its salt;and

(c) 5 to 40%, by weight, of an unsaturated quaternary ammonium compound.

The instant invention is also directed to a water soluble polymer,having an intrinsic viscosity of 0.05 to 2.5 prepared from:

(a) 50 to 90%, by weight, of an unsaturated carboxylic compound selectedfrom the group consisting of acrylic acid, methacrylic acid, their saltsand mixtures thereof;

(b) 5 to 40%, by weight, of an unsaturated sulfonic compound selectedfrom the group consisting of 2-acrylamido-2-methylpropylsulfonic acid,2-methacrylamido-2-methylpropylsulfonic acid, their salts and mixturesthereof; and

(c) 5 to 40%, by weight, dimethyl diallyl ammonium chloride, diethyldiallyl ammonium chloride and mixtures thereof.

The phrase "inhibiting the formation and deposition" is meant to includethreshold inhibition, dispersion, solubilization, or particle sizereduction.

The word "scale" includes any scale forming in an aqueous solution.Examples include calcium carbonate, calcium sulphate, calcium phosphate,calcium phosphonate (including calcium hydroxyethylidene diphosphonicacid), calcium oxalate, barium sulphate, silica, alluvial deposits,metal oxide (including iron oxide), and metal hydroxide, (includingmagnesium hydroxide).

The phrase "aqueous system" is meant to include any system containingwater; including, but not limited to, cooing water, boiler water,desalination, gas scrubbers, blast furnaces, sewage sludge thermalconditioning equipment, reverse osmosis, sugar evaporators, paperprocessing, mining circuits and the like.

Any unsaturated carboxylic acid or salt may be used to prepare thepolymer. Examples include acrylic acid, methacrylic acid, α-halo acrylicacid, maleic acid, itaconic acid, vinyl acetic acid, allyl acetic acid,fumaric acid, β-carboxyethyl acrylate, their salts and mixtures thereof.The preferred carboxylic acids are acrylic acid, methacrylic acid,β-carboxyethylacrylate, maleic acid, fumaric acid itaconic acid, andtheir salts. The most preferred carboxylic acids are acrylic acid,methacrylic acid and their salts.

Any unsaturated sulfonic acid or salt may be used. Examples include2-acrylamido-2-methylpropylsulfonic acid,2-methacrylamido-2-methylpropylsulfonic acid, styrene sulfonic acid,vinyl sulfonic acid, sulfo alkyl acrylate or methacrylate, allylsulfonic acid, methallyl sulfonic acid, 3-methacrylamido-2-hydroxypropyl sulfonic acid, sulfonic acid acrylate, their salts and mixturesthereof. The preferred sulfonic compounds are2-acrylamido-2-methylpropylsulfonic acid,2-methacrylamido-2-methylpropylsulfonic acid, allyl sulfonic acid,styrenesulfonic acid, vinylsulfonic acid and their salts. The mostpreferred sulfonic acids are 2-acrylamido-2-methylpropylsulfonic acid,2-methacrylamido-2-methylpropylsulfonic acid and their salts.

Any quaternary ammonium compounds may be used. Examples include dimethyldiallyl ammonium chloride (DMDAAC), diethyldiallyl ammonium chloride(DEDAAC), methacryloyloxyethyl trimethyl ammonium chloride (METAC),methacryloxyloxyethyl trimethyl ammonium methosulfate (METAMS),acryloyloxyethyl trimethyl ammonium chloride (AETAC), methacrylamidopropyl trimethyl ammonium chloride (MAPTAC), acryloyloxyethyl trimethylammonium methosulfate (AETAM), acrylamido methyl propyl trimethylammonium chloride (AMPTAC), and acrylamido methyl butyl trimethylammonium chloride (AMBTAC). The preferred quaternary ammonium compoundsare DMDAAC, DEDAAC and METAC. The most preferred quaternary ammoniumcompounds are DMDAAC and DEDAAC.

Mixtures of the various monomers may be used. Non-ionic monomers (suchas acrylamide, methacrylamide and acrylonitrile) may also be present inthe polymers. Terpolymers are preferred.

The polymers in the instant invention are prepared from 50 to 90%,preferably 60-75%, by weight, of an unsaturated carboxylic acid or salt;5 to 40%, preferably 5 to 25%, by weight, an unsaturated sulfonic acid,or salt; and 5 to 40%, perferably 10 to 25%, by weight, of a quaternaryammonium compound.

The polymers may be prepared by mixing the monomers preferably in thepresence of a free radical initiator. Any free radical initiator may beused. Examples include peroxides, azo initiators and redox systems. Thepolymerization may also be initiated photochemically. The preferredcatalysts are sodium persulfate and sodium metabisulfite or a mixture ofammonium persulfate and any azo type initiator, such as2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile).

The polymerization may be conducted by any of a variety of procedures,for example, in solution, suspension, bulk and emulsions.

The reaction temperature is not critical. The reaction will generallyoccur between 10 and 100° C., preferably 40 to 60° C. It is generallyimpractical to run the reaction below room temperature because thereaction is too slow. Above a temperature of 60° C., the molecularweight of the polymer tends to decrease. The reaction, depending on thetemperature, generally takes from 5 minutes to 12 hours. Measuring forresidual monomer will verify when the reaction is complete.

The pH of the reaction mixture is not critical. The pH is generally inthe range of 3.0 to 9.0.

The percent solids in the reaction mixture is not critical. Thepreferred range is 1 to 50%, by weight, solids.

The polymers are usually identified by intrinsic viscosity. Theintrinsic viscosity should be 0.05 to 2.5, preferable 0.05 to 0.5 dl/g,in 1.0 M sodium chloride (measured on a 75 Cannon Ubbelohde capillaryviscometer).

The polymers of the instant invention are used in a minimum dosage of0.1 ppm, preferably 0.1 to 100 ppm, most preferably 0.1 to 25 ppm.

EXAMPLES

The following abbreviations are used in the examples and are defined asindicated:

AA=acrylic acid.

AMPS=2-acrylamido-2-methylpropylsulfonic acid.

DMDAAC=dimethyldiallyl ammonium chloride.

METAC=methacryloyloxyethyl trimethyl ammonium chloride.

MAPTAC=methacrylamido propyl trimethyl ammonium chloride

Polymerization

The monomers were mixed in the ratios indicated in the Tables so as tomake up 28% of the total solution weight. Sufficient amount of sodiumhydroxide was added to neutralize the solution to pH 4.5. Sodiumpersulfate and sodium metabisulfite, as catalyst, were added to theneutralized monomer solution at 0.8 and 1.5 percent of the solutionweight respectfully. The initiation temperature was 25° C. Thepolymerization was allowed to run to completion which usually tookbetween 15 and 30 minutes at which time the reaction temperature hadpeaked between 80-90° C.

Intrinsic viscosities were measured in 1 M NaCl in a size 75 CannonUbbelohde capillary viscometer. Measurements at 2.0, 1.0, and 0.5 g/dlwere taken. The Huggins equation was used to determine the intrinsicviscosity.

Calcium Carbonate Inhibition

Calcium carbonate stabilization was determined by adding a givenconcentration of the polymers of the instant invention to a solutioncontaining 200 mg/1 Ca⁺² (as CaCl₂), 600 mg/1 HCO₃ ⁻¹ (as NaHCO₃) at pH8.0±0.1. The solution was stored in a stagnant flask for 24 hours at 60°C (140° F.). Poor performing samples allow a precipitate of CaCO₃ toform. To remove these `solids` the solution is filtered through a 2.5micron filter. The inhibitor effectiveness under these conditions isobtained by determination of the soluble calcium content of the testsolutions using the Schwarzenbach titration method (EDTA, chrome black Tindicator). The soluble calcium ion concentration in the absence ofinhibitor is equivalent to 0% scale inhibition. The percent inhibitionfor a given test is determined by: ##EQU1## Vo=the Schwarzenbachtitration volume with no inhibitor present (control) Vt=theSchwarzenbach titration volume when no precipitation occurs

Ve=the experimental Schwarzenbach titration volume when inhibitors arepresent in the test solution

Calcium Sulfate Inhibition

Calcium sulfate stabilization was determined by adding a givenconcentration of the polyampholyte of the instant invention to asolution containing 4800 mg/1 Ca⁺² (as CaCl₂) and 2000 mg/1 SO₄ ⁻² (asNa₂ SO₄) at pH 7.0±0.5. The solution was stored in a stagnant flask for24 hours at 60° C (140° F.). Poor performing samples allow CaSO₄precipitation to occur. To remove these `solids`, the solution isfiltered through a 2.5 micron filter. The inhibitor effectiveness underthese conditions is obtained by determination of the soluble calciumcontent of the test solution using the Schwarzenbach titration method(EDTA, chrome black T indicator). The soluble calcium ion concentrationin the absence of inhibitor is equivalent to 0% scale inhibition. Theparent inhibition for a given test is determined by: ##EQU2## Vo=theSchwarzenbach titration volume with no inhibitor present (control)Vt=the Schwarzenbach titration volume when no precipitation occurs

Ve=the Experimental Schwarzenbach titration volume

when inhibitors are present in the test solution

Calcium Phosphate Inhibition

Calcium phosphate stabilization was determined by adding a givenconcentration of the polyampholytes of the instant invention to asolution containing 200 mg/1 Ca⁺² (as CaCl₂) and 9 mg/1 PO₄ ⁻³ (as Na₂HPO₄). The solution is buffered at pH 8.5 by adding a 16.1% solution ofNaHCO₃ :Na₂ CO₃. This solution was stored for 24 hours at 60° C. (140°F.). Poor performing samples allow CaPO₄ precipitation to occur so thestored solutions are filtered through 2.5μ filter paper to remove`solids`. The inhibitor effectiveness under these conditions is obtainedby determination of the soluble phosphate content of the test solutionusing a photometric method (ascorbic acid as indicator). The range ofthe test is about 0 to 1.6 mg/1 phosphate when the color is measured ina 1-inch cell at a wavelength of 880 nm. Higher levels can be determinedby: (1) diluting the sample; (2) measuring the test color in a smallertube or cell; and/or (3) making the color measurement at 625 nm. Thepercent inhibition for a given test is determined by: ##EQU3##

    __________________________________________________________________________                                        CaPO.sub.4                                Composition           CaCO.sub.3 Inhibition                                                                  CaSO.sub.4                                                                         Inhibition                                            Quaternary                                                                          [h] (ppm Active)                                                                           2.5 ppm                                                                            (ppm Active)                              Examples                                                                           AA AMPS                                                                              Ammonium                                                                            (dl/g)                                                                            1.5                                                                              2.0                                                                              2.5                                                                              Active                                                                             5.0                                                                              10.0                                   __________________________________________________________________________                DMDAAC                                                            1    70 20  10    0.29                                                                              58 72 72 86   9  100                                    2    70 10  20    0.12                                                                              89 100                                                                              100                                                                              84   1  100                                    3    60 30  10    0.23                                                                              56 68 68 --   24 100                                    4    60 20  20    0.15                                                                              100                                                                              100                                                                              100                                                                              52   0  100                                    5    60 10  30    0.18                                                                              88 88 91 --   8   51                                    6    50 40  10        44 44 63      11 100                                    7    50 25  25        60 60 74      4  100                                    8    50 10  40        79 90 92      1   13                                                METAC                                                             9    60 20  20    0.24                                                                              60 62 62      6   77                                                MAPTAC                                                            10   60 20  20    0.27                                                                              27 33 40      6   84                                    __________________________________________________________________________

What is claimed is:
 1. A process for inhibiting the formation anddeposition of scale in aqueous systems, said scale including calciumcarbonate, calcium sulfate or calcium phosphate, and mistures thereof,comprising adding to the system at least 0.1 ppm of a water-solublepolymer having an intrinsic viscosity of 0.05 to 0.5 dl/g, preparedfrom: (a) 60 to 75%, by weight, of an unsaturated carboxylic compoundselected from the group consisting of acrylic acid, methacrylic acid andtheir salts;(b) 5 to 25%, by weight, of an unsaturated sulfonic compoundselected from the group consisting of 2-acrylamido-2-methylpropylsulfonic acid, 2-methacrylamido-2-methylpropyl sulfonic acid and theirsalts; and (c) 10 to 25%, by weight, of an unsaturated quaternaryammonium compound selected from the group consisting of dimethyl diallylammonium chloride and diethyl diallyl ammonium chloride.
 2. The processof claim 1, wherein 0.1 to 25 ppm of polymer is added.